Bicycles and ergometers are frequently used as training devices or as a medical device, for example for rehabilitation. The force and power output, which a user or a patient applies to his training device, are parameters, which are of interest for various reasons. These can be determined by measuring the torque, which the user applies via the pedal cranks to the bicycle. Training or medical data can be derived from the value of the applied torque, or an automatic gear shift can be initiated. Furthermore, the applied torque is a parameter, which can be displayed on a multipurpose display or bicycle computer for monitoring the use of the bicycle or ergometer.
German patent application DE 10 2007 040 016 A1 discloses a torque measurement device for an ergometer. The device is integrated in the bottom bracket bearing. The torque, which is induced in the bottom bracket shaft via a respective one of the pedal cranks being linked to this shaft, is determined. The torque transmission results in elastic torsion of the shaft. This torsion is subject to measurement. The applied torque is derived from the amount of torsion. The applied force or torque can be detected for both, the left and the right crank being driven by the left and right leg of the user, respectively. This separate acquisition of torque data, however, requires that the torque transmission is from the left end and from the right end of bottom bracket shaft to the center of the shaft. At the center of the shaft, a driving sprocket wheel or a pulley can be mounted. This particular design is, however, only applicable in ergometers. This derives from the fact that in almost every bicycle, the bottom bracket shaft carries the driving sprocket wheel proximate to one of the ends of the shaft, i.e. near to the left or right pedal crank. Within a bicycle having this type of bottom bracket shaft, the torque measurement device only captures the torque, which is applied via the pedal crank, which is opposite to the driving sprocket. The torque of this pedal crank is transmitted to the sprocket via the bottom bracket shaft and is therefore accessible. In other words, the torque measurement device according to reference DE 10 2007 040 016 A1 is only suitable for determination of the torque, which is applied via either the left or the right pedal crank.
Another prior art torque measurement device is disclosed in German utility model DE 20 2007 019 291 U1. A bottom bracket shaft having a first and a second hollow shaft member, which are rotationally fixed to one another, incorporates a torque sensor device within one of the shaft members. The induced torque is acquired using a magnetic sensor device. The torque measurement device is, however, only designed for acquisition of torque, which is applied via one of the two pedal cranks. As a result, the applied torque of only one leg of the user of the bicycle may be determined.
For pedelecs or e-bikes, it is desirable to have access to the torque, which is applied via both legs of the user. The applied torque can serve as a parameter for the control of an auxiliary electric drive. For example, the drive can be activated, when the applied torque exceeds a certain threshold. In addition to this, it is desirable to have a value for the torque at hand, which is applied by the auxiliary electric drive. This may serve as a value for overload protection.